Method and apparatus for evacuating vessels



May 24, 1966 J. R. JONES ETAL METHOD AND APPARATUS FOR EVACUATING VESSELS Filed May 20. 1963 ATTO NE VS United States Patent 3,252,264 METHOD AND APPARATUS FOR EVACUATING VESSELS John Roger Jones, Manhattan Beach, and Maciej .lerzy Makowski, Torrance, Califi, assignors to Fairchild Hiller Corporation, a corporation of Maryland Filed May 20, 1963, Ser. No. 281,547 11 Claims. (Cl. 53-7) ture sensitive alloy, such as solder. An evacuation fixture is provided which is capable of heating the alloy to break the seal and then removing the cap from the vessel. The fixture provides communication between the interior of the vessel and a vacuum source while preventing communication between the vessel interior and the atmosphere. After the desired vacuum has been established the fixture replaces and reseals the cap to the vessel.

While the present invention can be used in evacuating many types of vessels it has proved to be particularly useful in evacuating or re-evacuating cryostats which are used in low temperature cryogenic systems. It has been found that the operation of a cryogenic system is greatly enhanced when the cryostat is kept to as near vacuum condition as possible. Since all evacuated vessels including cryostats have leaks which let in surrounding atmosphere which reduces the vacuum, it becomes necessary to re-evacuate the cryostat vessel to maintain the efiiciency of the cryogenic system. The present invention provides a method and apparatus for evacuating the vessels in both a relatively simple and practical manner.

It is therefore an object of the invention to provide a method and apparatus for evacuating vessels.

A further object of the invention is to provide a novel seal for a vessel and a fixture to remove the seal whereby evacuation of the vessel may be readily accomplished.

Still another object "of the invention is to provide a vessel having a cap sealed thereto by a heat sensitive material and a fixture for removing the cap and providing communication to a vacuum source while preventing communication with the atmosphere.

A further object of the invention is to provide a fixture tor removing the seal from a vessel and introducing a vacuum therein.

Other objects and advantages of the present invention will become more apparent upon reference to the following specification and annexed drawing in which:

FIGURE 1 is a cross-section of the vessel and evacuating fixture illustrating the present invention; and

FIGURE 2 is a cross-section of a portion of the vessel and fixture taken with the cap removed.

Referring to FIGURE 1, a vessel is shown which is to be evacuated or re-evacuated by the method and apparatus of the present invention. The vessel 10 may illustratively be a cryostat in which a low temperature gas in liquid form is circulated to 0001 other equipment. The vessel 10 is of generally cylindrical shape, although any suitable shape may be utilized.

The end wall 11 of the vessel has a circular or other shaped opening 12 therein and a shoulderor lip 13 surrounding the opening on the outer surface of the end wall. The shoulder 13 is made of metal, as may be all 3,252,264 Patented May 24, 1966 a metal cap 14 which is held fixed to the shoulder 13 by a quantity of a heat sensitive alloy 15 such as solder.

The cap 14 has a bottom piece 16 to cover the opening 12 and an inner side wall 17 which fits within the raised shoulder 13. An annular slit 18 is provided in the cap so that it can fit over the shoulder 13. The cap also has a groove 19 on the inner surface of the outer Wall 20 surrounding the shoulder 13. The groove 19 is used 7 to hold and attract the alloy 15 which is used to seal the cap to the shoulder. In order to complete the cap structure an extending wall piece 22 is provided with internal screw threads 23. The function of this wall piece and the threads is described below. It should be clear that when the alloy 15 is melted and then permitted to harden that the cap 14 will seal the vessel opening. Similarly, when the alloy is in molten form, the cap may be removed from or placed onto the shoulder 13.

When it becomes necessary to evacuate or re-evacuate the vessel, the cap 14 must be removed so that access can be had to the interior of the vessel to exhaust the gases therein and produce the degree of vacuum desired. This is accomplished by an exhaust fixture 30 having a housing 31 with a port 32 therein for connection to a suitable exhaust pump (not shown). One end of the exhaust fixture 36 is adapted to fit over the cap 14 and be fixedly fastened to the end 11 of the vessel by a flange 34. The flange 34 preferably mates .with adepressed wall 35 on the end of the vessel and is fastened thereto by a number of bolts 36 which screw into threaded holes 37 on the vessel. A sealing ring 38 is provided between the stepped ends of the fixture and the vessel to improve the seal therebetween.

The other end of the evacuating fixture 30 is equipped with a closure plate which, for ease of manufacture, is formed by two separate pieces 40 and 41. Piece 41 of the closure plate is fastened to piece 40 by a number of bolts 42 around the edges thereof while piece 40 is fastened to the housing 31 by bolts 43. Closure piece 41 has internal threads 45 which accommodate the mating threads 46 on a hollow shaft 47. One end 48 of the shaft 47 extends through the housing so that the shaft may be notated for the purpose to be described.

The closure piece 41 is also provided, with an aperture 49 which communicates with the interior of an ex: pandible bellows chamber 50 mounted within the housing of the evacuating fixture. One end 52 of the bellows is fastened to the closure piece 40 while the other end 53 is fastened to the flanged Wall 54 of a hollow piece 55. The other end 57 of piece is closed and of a size to mate with the bottom and inner side wall of cap 14 while its outer wall is provided with external screw threads 58 to mate with the screw threads 23 on the cap.

The end 59 of the shaft 47 within the housing is flanged for rotatable mounting on the flanged wall 54 of piece 55. The flange is held by a ring 61 having a raised lip 62. The ring is held to piece 55 by a number of bolts 63 which screw into threaded holes on the piece. Since the end 59 of the shaft rotates within the ring 61, rotation of the shaft 47 causes the bellows 50 to expand or con tract and also causes piece 55 to move along with the end 59 of the shaft and With relation to the end of fixture 39 adjacent the vessel.

A cartridge heater 65 is located within the end 59 of hollow shaft 47 and the hollow piece 55.. The heater engages the wall and bottom 57 0f piece 55 so that heat may be conducted from the heater to the piece 55 and then to cap 14. Current is provided to the heater through leads 66 and 67 which are brought out through the end 48 of the shaft.

In order to evacuate the vessel 10 the following is 'done. With the fixture spaced away from the vessel and not attached thereto, the shaft 47 is turned until it is in its extreme extended position within the housing 31 of the evacuating fixture 30. At this point the piece 55 will abut the end of housing 31 and will be held stationary by friction. The fixture 30 is then placed over the end Wall 11 f the vessel with the external threads 53 of the piece 55 engaging the internal threads 23 of the cap 14. The fixture is then turned, until the threads 23 and 58 are fully engaged. At this time the bellows 50 is fully extended. However, the bellows will not rotate because of the torsional rigidity of the bellows 50.

The sealing member 38 having been'previously placed in position between the end wall 11 and the fixture, the fixture and threads 53 are backed otf until the bolt holes in the fixture mounting flange and the bolt holes 37 in the vessel end wall 11 are brought into alignment. When this is done the fixture is fastened to the vessel by the bolts 36 previously referred to.

Once the seal is made between the end of the fixture and the vessel, vacuum is supplied through the port 32. Now, since the end of the vessel is effectively sealed to the atmosphere by the fixture and communication is only with the vacuum source, cap 14 may be removed.

To remove the cap, the heater 65 is energized and heat is conducted to the cap 14 to melt the solder which holds the cap to the lip of the vessel. After sufficient time has elapsed to permit the solder to become molten, the shaft 47 is rotated in a direction to move it out of the housing. FIGURE 1 shows the shaft in an intermediate condition with the threads of piece 55 and the cap engaged. Because of the rotation of the shaft flange end 59 in the ring 62, the threaded engagement between the piece 55 and the cap is not disturbed. Therefore as the shaft is withdrawn out of the housing the piece 55 moves away from the vessel taking the cap 14 with it. When the cap is removed from the opening 12, communication is made between the interior of the vessel and the vacuum source. This is shown in FIGURE 2 in which the arrows indicate the direction of exhaust flow from the vessel. At this time the bellows 50 is contracted. The heater 65 is normally de-energized after the cap is removed and the exhausting process is taking place.

The evacuation of the vessel is carried out in the normal manner until the desired degree of vacuum is achieved. In order to reseal the vessel it is only necessary to turn the shaft 47 in a direction to move the cap 14 back onto the lip 13 of the vessel and have the piece 14 abut 11. This is done after the heater 65 is turned on so that the solder in the groove 19 of cap 14 is in a moten state. Once the cap is secured to the lip of the vessel the heater 65 is turned off and the solder is permitted to solidify. This re-establishes the seal of the vessel by the cap. The vacuum source is then disconnected and the bolts 36 are removed. This permits the fixture to be unscrewed from the cap.

It should be understood that the groove 19 in the cap 14 which holds the solder is so dimensioned that capillary attraction will prevent the molten solder from flowing out of the groove. Similarly, when the solder is melted it has a tendency to draw and congregate around and in the groove. This same effect may be accomplished in any of a number of suitable ways.

Therefore it can be seen that a novel structure and method is provided which can effectively be used to evacuate different types of vessels including those of the so-called cryostat type which operate in low temperature refrigeration systems. The evacuation of such avessel is carried out in a relatively simple manner by the present invention by the cooperation of the evacuation fixture and the solder seal used for the vessel sealing cap.

While preferred embodiments of the invention have been described above, it will be understood that these are illustrative only, and the invention is limited solely by the appended claims. I

What is claimed is:

1. An evacuation system for a vessel having an opening therein which is covered by a cap adapted to be sealed to the vessel -by a quantity of heat sensitive material comprising an evacuation fixture adapted to fit over the end of said vessel having the cap to prevent entry of ambient gas into said vessel opening and to provide a gasfree atmosphere, heating means in said fixture adapted to heat said heat sensitive material and melt the same, and means to withdraw the cap from said vessel when the heat sens-itive material is in the molten state, said last named means operating in the gas free atmosphere provided by. said evacuation fixture.

2. An evacuation system for a vessel having an opening therein which is covered by a cap adapted to be sealed to the vessel by a quantity of a heat sensitive material com- .prising an evacuation fixture adapted to fit over the end of said vessel having the cap to prevent entry of ambient gas into said vessel opening and to provide a gas-free atmosphere, said fixture having means therein for engaging said cap, heating means in said fixture adapted to heat said heat sensitive material and melt the same, means for moving said engaging means to withdraw the cap from said vessel when the heat sensitive material is in a molten state and to replace the cap thereon, and means sealing off said moving means from the gas free atmosphere provided by said fixture.

3. An evacuation system for a vessel having a metal portion surrounding an opening therein said opening being covered by a metal cap adapted to the sealed to the vessel by a quantity of a heat sensitive material comprising an evacuation fixture adapted to fit over the end of said vessel having the cap to prevent entry of ambient gas into said vessel opening and to provide a gas-free atmosphere, said fixture having means therein for engaging said cap, said last named means having a hollow portion, heating means in the hollow portion of said cap engaging means in heat condutoting relationship therewith, said heating means being adapted to heat said temperature-sensitive material on said cap and melt the same, means extending outside of said fixture dor moving said engaging means to withdraw the cap from said metal portion when the heat sensitive material is in a molten state and to replace the cap thereon, and bellow means sealing off said shaft from the gas-free atmosphere provided .by said evacuation fixture.

4. An evacuation system as provided in claim 3' wherein said cap has a groove therein to retain a quantity of the heat sensitive material.

5. An evacuation system comprising a vessel having a metal portion surrounding an opening therein, a metal cap for sealing said opening, a quantity of a heat sensitive material for fastening said cap to said metal portion, an evacuation fixture adapted to fit over said cap and a portion of said vessel to prevent entry of ambient gas into said vessel opening and to provide a gas free atmosphere, said fixture having means in said gas-free atmosphere for engaging said cap, heating means in heat-condulcting engagement with said cap adapted to heat said temperaturesensitive material and melt the same, and means for moving said engaging means to withdraw the cap from said metal portion when the heat sensitive material is in a molten state.

6. An evacuation system comprising a vessel having a metal portion surrounding an opening therein, a metal cap do"): sealing said opening, a quantity of a heat sensitive material for fastening said cap to said metal portion, an evacuation fixture adapted to fit over said cap and a port-ion of said vessel to prevent entry of ambient gas into said vessel opening and to provide a gas-free atmosphere, said fixture having means therein for engaging said cap, heating means in heat-conducting engagement with said cap, said heating means being adapted to heat said temperature-sensitive material and melt the same, a shaft extending outside of said fixture for moving said engaging means, means for sealing off said shaft from the gas-free atmosphere provided )by' said fixture, said shaft being freely rotatable with respect to said engaging means whereby rotation of said shaft moves said engaging means to withdraw the cap from said metal portion when the heat sensitive material is in a molten state and to replace the cap thereon.

7. An evacuation system for a vessel having a metal lip portion surrounding an opening therein which is to be sealed by a metal oaip fitting over said lip, said cap having a wall portion with screw threads and a quantity of a heat sensitive material for fastening said cap to said metal lip to seal said opening comprising an evacuation fixture adapted to fit over a portion of said vessel containing said cap to prevent entry of ambient gas into said vessel and to provide a gas-"free atmosphere Within said fixture, said fixture having means adapted to communicate with an exhaust system, an end piece with screw threads for engaging the screw threads on said cap, a shaft freely rotatably mounted with respect to said end piece at one end thereof, said shaft and said fixture having means to permit said shaft to he moved in and out of said fixture thereby moving said end piece, heating means for heating said heat sensitive material to melt the same, a bellows mounted hetween said end piece and one end of the fixture to seal off the shaft from said gas-free atmosphere Within said fixture, the rotation of said shaft out of said fixture withdrawing the cap from the lip of the vessel and the rotation of said shaft into the fixture placing the cap back onto said lip.

8. An evacuation system comprising a vessel having a metal lip portion surrounding an opening therein, a metal cap fitting over said lip and sealing said opening, said cap having a wall portion with threads, a groove on the cap for holding a quantity of a heat sensitive material for fastening said cap to said metal portion to seal said opening, an evacuation fixtuer adapted to fit over a portion of said vessel containing said cap to prevent entry of ambient gas into said vessel and to provide a gas-free atmosphere Within said fixture, said fixture having means adapted to communicate with an exhaust system, an end piece with screw threads for engaging the threads on said cap, a shaft freely rotatably mounted wit-h respect to said end piece at one end thereof, said shaft and said fixture having mating threads to permit said shaft to he moved in and out of said fixture thereby moving said end piece, heating means in heat conductive engagement with said end piece, said heating means being adapted to heat said heat sensitive material and melt the same, a [bellows mounted between said end piece and one end of the fixture to seal off 6 the shaft from said gas free atmosphere within said fixture, an opening on said end of the fixture to provide communication between the interior of said bellows and the ambient atmosphere, the rotation of said shaft out of said fixture withdrawing the cap from the lip of the vessel and the rotation of said shaft into the fixture placing the cap back onto said lip.

9. The method of evacuating a vessel having a cap to i 'be sealed over an opening thereof by a heat sensitive material comprising the steps of covering the sealed end of the vessel to prevent communication thereof with ambient gas, providing a gas-free atmosphere within said fixture, withdrawing the cap from the opening inthe gas free atmosphere, introducing a vacuum into the vessel, heating the cap to melt the heat sensitive material thereon to place said material in a molten state, placing the cap onto the vessel to cover the opening, and cooling the heat sensitive material to sea-l the cap to the vessel.

10. The method of evacuating a vessel having a cap sealed to an opening thereof by a quantity of heat sensitive material comprising the steps of covering the sealed end of the vessel to prevent communication thereof with ambient gas, providing a gas-'free atmosphere within said fixture, melting the heat sensitive material which seals the cap to the opening, withdrawing the cap [from the opening in the gas-ifree atmosphere, introducing a vacuuminto the vessel, reheating the heat sensitive material to place said material in a molten state, placing the cap balck onto the vessel to cover the opening, and cooling the heat sensitive material to seal the cap to the vessel.

11. The method of evacuating a vessel having a heat conductive cap sealed to an opening thereof by a quantity of heat sensitive material comprising the steps of covering the sealed end of the vessel with a fixture, exhausting the fixture to provide a gas-free atmosphere, heating the cap to melt the heat sensitive material which seals the cap to the opening, withdrawing the cap from the opening in the gas-free atmosphere, introducing a vacuum into the vessel, reheating the leap to melt the heat sensitive material to place said material in a molten state, placing the cap hack onto the vessel to cover the opening, and cooling the heat sensitive material to harden the same thereby sealing the cap to the vessel.

References Cited by the Examiner UNITED STATES PATENTS 2,780,899 2/1957 Benson et a1. 53-80 X 3,114,690 12/1963 Butler 53-12 X TRAVIS S. MCGEHEE, Primary Examiner. 

9. THE METHOD OF EVACUATING A VESSEL HAVING A CAP TO BE SEALED OVER AN OPENING THEREOF BY A HEAT SENSITIVE MATERIAL COMPRISING THE STEPS OF COVERING THE SEALED END OF THE VESSEL TO PREVENT COMMUNICATION THEREOF WITH AMBIENT GAS, PROVIDING A GAS-FREE ATMOSPHERE WITHIN SAID FIXTURE, WITHDRAWING THE CAP FROM THE OPENING IN THE GAS-FREE ATMOSPHERE, INTRODUCING A VACUUM INTO THE VESSEL, HEATING THE CAP TO MELT THE HEAT SENSITIVE MATERIAL THEREON TO PLACE SAID MATERIAL IN A MOLTEN STATE, PLACING THE CAP ONTO THE VESSEL TO COVER THE OPENING, AND COOLING THE HEAT SENSITIVE MATERIAL TO SEAL THE CAP TO THE VESSEL. 